IBM (IBM is a trademark of International Business Machines Corporation registered in many countries around the world) has a product called LTFS (Linear Tape File System) as a file system that runs on a tape device.
Some versions can be downloaded for free from a web site as software or a program cooperating with hardware, and other versions are sold.
LTFS is an open standard, and multiple companies are doing business with products adopting the LTFS standard.
FIG. 1 is a schematic diagram of usages of data bands and wraps on a tape medium adopting an LTO (Linear Tape-Open) as a conventional technique.
The tape medium adopting the LTO standard is divided into areas called four data bands as in FIG. 1.
When a tape drive writes data to the tape medium, the tape drive reciprocates a tape with a total length of a few hundred meters a few dozen times to write an amount of data corresponding to the prescribed capacity of the tape medium.
Although simplified in FIG. 1, the tape is actually reciprocated about ten times per data band (the number of reciprocations differs depending on the generation of the format).
This one way is called a “wrap.”
All wraps are numbered. The wraps used to read and write data while traveling the tape medium in the forward direction have even numbers, and the wraps used to read and write data while traveling the tape medium in the backward direction have odd numbers.
When writing data and when reading written data serially, the tape medium can read and write data at a transfer rate of about 160 MB/sec.
On the other hand, when plural pieces of data existing in any positions are read, since the length of the tape medium is about 800 m, a seek time of one minute on average or about two minutes at most is required for the travel between pieces of data.
In other words, when discrete pieces of multiple data existing at any positions are read, the transfer rate is significantly reduced. It can be said that the cause is the seek time required.
The emergence of LTFS enables users of tape media to write and read files to and from the tape media directly via a file system without through dedicated backup software or a hierarchical storage system.
Therefore, more and more users who did not use tape media in the past have begun using the tape media.
In a hospital, various kinds of data that range from data of a small size, such as name, sex, and age in an electronic medical record or the like, to data of a large size, such as an X-ray image or video taken with an endoscope are used.
Although it has been conventionally common practice to manage such kinds of data in a hard disk drive (HDD), the introduction of LTFS to manage data is being considered because the threshold to use tape media through the LTFS has been lowered.
As the characteristics of data handled in a hospital, multiple methods of using data exist.
As an access pattern used in medical examination and treatment, there is a pattern of access to plural kinds of data (e.g., name, sex, age, an X-ray image, and endoscopic video) in units of patients.
On the other hand, as an access pattern for academic use, there is a pattern of access to specific data (e.g., X-ray images) across multiple patients.
When random access occurs in data reading, the transfer rate in data reading is significantly reduced irrespective of whether the storage destination of data is a tape medium or an HDD.
Thus, there is a reduction in reading transfer rate caused by random access that occurs when there are multiple access patterns for using data.
Patent Literature 1 is made by the same applicant as this application, and it is meaningful as a reference to understanding a writing method adopted as a prerequisite in the present invention.
In Patent Literature 1, data are written by paying attention only to one rectangle (a singular file of each of name, sex, age, X-ray image, and endoscopic video) as shown in FIG. 6 of the present application (to be described in detail later) only to intend to read data vertically.
To summarize a difference between (features of) Patent Literature 1 and the present invention, the present invention also considers a landscape-oriented rectangle as shown in FIG. 5 of the present application to write data to a tape medium in a manner to make it easy to read the data along both the landscape orientation (along the landscape-oriented rectangle) and the portrait orientation (along the portrait-oriented rectangle).
In other words, in the present invention, data are written by paying attention to two-dimensional arrangement on the assumption of use in multiple access patterns.    [Patent Literature 1] Japanese Patent Application Publication No. 2013-191259